Conventional methods and apparatus for testing radio frequency integrated circuits (RFIC) require the use of radio frequency (RF) contacts. For example, a wafer containing unsingulated RFIC chips (dies) may be placed on a probe station whereupon a probe is used to make contact with each RFIC. Once this connection is established, interrogating signals modulated on an RF signal are fed into the RFIC, and the responses (the returned signal) are analyzed in order to determine whether the RFID functions properly. Alternatively, the RFIC's may first be singulated from the wafer and packaged in plastic packages. The RF test can then be performed by placing the packaged chip on a "load board." Such load boards comprise circuit boards containing fixtures for mounting the packaged RFIC in a temporary manner and a circuit for feeding an RF interrogation signal into the packaged RFIC to facilitate testing.
In either testing method, the RF interrogating signals are sent from a tester to the RFIC through a cable (e.g., a coaxial cable). Thus, the entire testing circuit consists of wired connections, and the testing signals (i.e., the interrogating signal and the responded signal) are well contained in a guide wave structure. While use of such "wired" test apparatus and methods provides satisfactory testing of most RFIC's, some functionalities of radio frequency identification integrated circuits (RFID IC) require a "wireless" RF test (i.e., a "field" test). For example, some circuits of the RFID IC, which are supposed to operate in the RF field, may appear to be functioning properly with the conventional wired test methods, but may later be found to be functioning improperly when packaged into RFID transponders and placed in an RF field where the RF signal is contaminated with noises and suffers from distortions caused by the time-varying characteristics of the wireless link and interference from surrounding objects. Similarly, it is difficult to determine whether the memory of the RFID IC's will be properly written in the field even though they can be properly written using the wired testing methods. Further, the read distance of an RFID IC (or an RFID transponder) can only be truly determined through a wireless RF test with appropriate calibration. It is therefore desirable to provide a method and apparatus for performing wireless radio frequency testing of RFID IC's so that they may be more fully characterized and tested.